Timing control system



May 18, 1943 s. E. UNDY 2,319,524

TIMING CONTROL SYSTEM Filed Feb. 27, 1941 INVENTOR 'zzsidl Z. Und g ORNEYS.

- Patented May 18, 1943 TIMING comm. SYSTEM Gustav E. Undy, Detroit,Mich, assignor to Weltronic Corporation, Detroit, Mich., a corporationof Michigan Application February 27, 1941,'ScrialNo. 830,954;

. 15 Claims. (01. 2509-27). tween which the work l8 to be welded may beThe present invention relates to electrical control systems and, asherein disclosed, is specifically directed to the provision of improvedmeans for practicing the system for electric welding disclosed andclaimed in the co-pending application of the present applicant andChester F. Leathers, Serial No. 380,830, filed February 2'7, 1941. Incertain of its aspects, the present invention is an improvement upon theinvention described and claimed in the co-pending application of thepresent applicant, Serial No. 374,951, filed January 17, 1941.

The principal objects of the present invention are to provide a controlsystem of the above generally indicated character, which is simple inarrangement, reliable in operation, and which enables the delivery tosingle phase ,work circuits of balanced current components drawn from amultiphase system; to provide such a system employing a plurality ofsequentially operated control valves which function to control loadrectifiers in such relation as to deliver alternately opposite impulsesof load current, each made of lowing description and in the appendedclaims,

preferred but illustrative embodiments of the invention are shown in theaccompanying drawing, in which:

Figure 1 is a diagrammatic view of circuits embodying the invention; and

Figure 2 is a diagrammatic view illustrative of current conditions.

It will be appreciated from a complete understanding of the presentinvention that, in a generic sense, the improvements thereof may beutilized for various specific purposes, and that various changes in thearrangement of parts may be made. For reasons which will be apparent tothose skilled in the welding art, the present system has particularvalue and utility in the welding field, and is so disclosed herein.

Referring particularly to Fig. 1, the secondary winding of theillustrative welding transformer WT is connected in a local circuit,which includes clamped. As will be understood, suitable means maybe-p'rovided to controlthe clamping pressure betweenthe electrodes [2and II. One terminal of the primary winding l8 of the weldingtransformer WT is connected to the center point of the star connectedsecondary winding of the three-phase supply transformer ST. The otherterminal of the primary winding i8 is connected to the cathodes of aseries of rectifiers 22, 24 and 26, and is connected to the anodes of acooperating series of rectiiiers 28, and 32. The rectiflers 22 and 28are reversely connected with respect to each other and are individual tothe sec-' ondary winding A of the supply transformer. The other pairs ofrectifiers 24-30 and 2632 are correspondingly connected, and areindividual, respectively, to the secondary phases B and C of the supplytransformer. As is indicated, the secondary phase B is reverselyconnected, so that currents and voltages in the several phases A, B andC are displaced 60 electrical degrees apart,

in the relation indicated in Fig. 2, in which figure sure a more uniformbalance between the loads on the respective phases of the source, themagnetic circuit of each primary winding and its cooperating secondarywinding are magnetically independent of the magnetic circuits for theother primary and secondary windings.

In a generic sense, the rectifiers 22 through 32 can be of any usualgaseous discharge type, but' may be and are herein illustrated as beingof the type known commercially under the tradename Ignitron." As will beunderstood, such rectifiers comprise an anode a, a reconstructing typecathode c of mercury or the like, and an igniter or control electrode i,which is permanently immersed in the cathode. Such devices have thecharacteristic of being normally nonconducting. If, however, a criticaligniting potential is applied between the igniter i and the cathode c ata, time when the anode a is positive with respect to the cathode c, thedevice becomes the illustrative welding electrodes l2 and M, be-

conducting and remains so for the balance of v the corresponding halfcycle of current flow. At

th conclusion of the just-mentioned half cycle of current flow, thegaseous atmosphere within the rectifier tends to rapidly becomedeionized,

, and if the application of a positive potential bemately 30 electricaldegrees are usually regarded as a suflicient deionizing interval forrectifiers having capacities suitable for welding purposes, and thepresent control system is so arranged as to delay the re-application ofa positive potential to the anode of each rectifier after the conclusionof a conducting half cycle thereof, for periods sufiiciently long toinsure complete deionization thereof.

As is described in more detail below, the rectifiers 22 through 32 arefired in the order 22, 24, 26, 28, 39 and 32, and this firing action iscontrolled by a series of firing valves VI, V2, V3, V4, V5, and V6,which are individual, respectively, to the just-mentioned rectifiers.The actuation or firing of the valves VI through V5, in turn, iscontrolled by a. corresponding series of control valves V1, V8, V9,VIII, VII, and VI2, and by an intermediate or bridging control valveVI3. The valves VI through VI3 may be and preferably are of a usual gasfilled type, each having an anode a, a cathode c and a grid or controlelectrode g. As will b understood, these valves are normallynon-conducting. If, however, a critical potential is applied to the grid9 at a time when the anode of the corresponding valve is positive, to apredetermined degree, with respect to the cathode, the valve becomesconducting and remains so for the balance of the corresponding halfcycle of current flow. The valves VI through V8 and V8 through VI3 arerendered normally non-conducting by applying negative biases to thegrids thereof, and to simplify the drawing, the means for applying suchbiases are indicated in the drawing by the reference characters DCIthrough DC6, and D08 through DCI3. The just- 4 mentioned biasing meansmay take any usual form.

The remaining control valve V1 is not provided with negative gridbiasing means, but the plate circuit of this valve is maintained in anormally de-energized condition by th normally open switch S, describedbelow. The grid potential of the valve V1 is controlled by a transformerT4, which may be and preferably is of the peaking type. The primarycircuit of the transformer T4 is provided with conventional phaseshifting elements, illustrated as comprising a condenser 34 and avariable resistor 36, and is supplied with power from a controltransformer TI, the primary winding whereof is connected across thesecondary transformer phase A. The terminal connnections betweentransformers TI and T4 are indicated by the reference characters a andb. The valve V1 is also provided with a blocking condenser 01, inaccordance with the disclosure of said copending application, and withassociated control elements comprising the auxiliary rectifier VI4 and ausual discharge valve VI 5.

The plate circuit of valve V1 is supplied with current from thepreviously mentioned transformer TI, and the plate circuits of valvesVII) and VI3 are also supplied from transformer TI. The plate circuitsof valves V8 and VII are supplied from a similar control transformer T2,the

primary winding whereof is connected across the secondary phase B, andvalves V9 and VI I are supplied with current from a similar controltransformer T3, the primary winding whereof is connected across thesecondary phase C.

The valves V8, V9, VI3, VIII, VII and VI2 are sequentially renderedconducting after valve V1 is rendered conducting, each said valve beingrendered conducting as a consequence of the conducting condition of thepreceding valve in the series, and for this purpose additional controltransformers TI4 through TI9 are provided.

It is thought that the remaining details of the invention may best beunderstood from adescription of the operation thereof. Assuming it isdesired to condition the system for operation, the line switch LS may beclosed, which thereupon connects the primary winding of the three-phasetransformer ST to the line conductors Ll, L2, and L3. This actionenergizes the secondary windings A, B and C. The winding A energizes thecontrol transformer TI and the usual heater transformer HT, the windingB energizes the control transformer T2, and the winding C energizes thecontrol transformer T3. The windings A, B and C further apply potentialsacross the associated pairs of rectifiers, which actions are, however,without effect since such rectifiers are in a non-conducting condition,and consequently no current is delivered to the welding transformer WT.

The energization of the heater transformer HT applies heating current tothe cathodes of the valves VI through VI4, which relation is indicatedby the reference character :1: applied to the secondary terminals of thetransformer HT and to the cathodes of the just-mentioned valves. Thisaction, however, does not render any of valves VI through V6 and valvesV8 through VI 3 conducting, because of the previously mentioned negativegrid biases applied thereto by the biasing means DCI, etc.

The energization of control transformer T2 energizes the platetransformers T8 and TI I associated with valves V8 and VI I, and theenergization of control transformer T3 correspondingly energizes theplate transformers T9 and 'II2 associated with valves V9 and VI2. Theseactions are, however, without effect in view of the negative grid biasesapplied to these valves, as aforesaid. The polarities of the energizingpotentials are indicated by the reference characters a and b applied tothe respective transformer terminals.

The energization of control transformer TI prepares a circuit for theplate transformer T], which circuit is, however, interrupted at the nowopen contact members of the starting switch S, and also completes acircuit for the plate transformers TI 0 and TI3, associated with valvesVI!) and VI3. These valves are, however, maintained in a non-conductingcondition by the aforesaid negative grid biases.

The energization of control transformer TI also energizes the peakingtransformer T4, and it will be understood, therefore, that at a criticalstage, relative to each half cycle of the voltage across the secondaryphase A, transformer T4 develops its maximum or critical potential,which maximum or critical potential is suflicient to apply a conductingpotential to the grid of valve VI. Preferably and as is diagrammaticallyindicated in Fig. 2, the phase shifting elements 34 and 36 are soadjusted, in relation to the other electrical quantities in the gridcircuit of valve V1, that the just-mentioned critical potential oftransformer T4 is developed at a point which coincides with thehypothetical zero point of the welding load current in phase A. It willbe understood, of course, that by reason of the inductive character ofthe welding load, the welding load current in phase A lags rathersubstantially behind the voltage across phase A. The successiveapplications of the conducting potential to the grid of valve V'l are,however, without effect so long as the starting control switch S ismaintained in the open position, since this switch interrupts theenergizing circuit for the plate transformer T1 associated with valveV1.

Assumingitisdesiredtoperformawelding operation, the switch S may beclosed, and it will be appreciated that closure of switch 5 may beeffected either manually or automatically. For example, switch S maycorrespond to. the contact members a of the switch, designated WC in thecopending application of Cletus J. Collom, Serial No. 358,473, filedSeptember 26, 1940, and assigned to the Weltronic Corporation, and theenergize.- tion of the operating winding for switch 8 may be efiected inthe manner disclosed in the iustmentioned copending application.

Closure of the switch S immediately energizes the transformer T1, theenergizing polarities being such that transformer T1 renders the plateof valve V1 positive with respect to the cathode thereof during halfcycles in which the anode of rectifier 22 is positive with respect tothe cathode thereof. For the purposes of the present decription, suchhalf cycles in which the anodes of rec tifiers 22, 24 and 26 arepositive maybe referred to as the positive half cycles and the termnegative half cycles may be used to refer to those half cycles in whichthe anodes of rectifiers 28, 30 and next positive half cycle of phase Afollowing the half cycle in which switch S is closed, transformer T4develops its critical potential and applies a' conducting potential tothe grid of valve V1 and this point, as previously mentioned, preferablycoincides with the hypothetical zero point of the load current in phaseA. At the time in question, the voltage of transformer Tl, which is inphase with the voltage of phase A, is high enough to pass currentthrough valve V'I.

voltage of phase A, and at the time in question enables transformer Tlto'deliver charging current to the blocking condenser Cl through acircuit which includes the auxiliary rectifier V. Condenser Cl ispreferably proportioned so that it receives the full charge in arelatively small fraction of the positive half cycle in question, and ascondenser C1 approaches its full charge, the potential app ed thereby tothe discharge tube VI! breaks down the latter and renders it conducting,tl1ereby applying a strong negative bias to the grid of valve W. Thisaction does notinterfere with the flow of current through valve V'lduring the balance of the half cycle in question, but it does preventvalve W from being again rendered conducting until such time ascondenser C1 has completely discharged itself through the localdischarge circuit provided therefor and including the resistor RI. Thetiming out of such condenser Cl, as described below, makes possible theinitiation of the next successive positive impulse of current deliveredto the welding circuit.

The potential across the resistor R, which exists during the time thatvalve V1 is in a conducting condition, applies a corresponding potentialto the primary winding of the sequence transformer TH, associated withvalve V8, which transformer is consequently rendered effective toovercome the negative bias normally applied to the grid of valve V8 bythe biasing means DCB associated therewith. As will be noted from Fig.2, current and voltage conditions in-phase A are displaced 60 electricaldegrees in advance of the '32 are positive with respect to the cathodesthereof. At a predetermined point (tl, Fig. 2) in the correspondingconditions in phase 'B, and at the time transformer T8 renders the plateof valve V8 positive, the voltage of transformer TM is still high enoughto apply a conducting potential to the grid of valve V8. Consequently,at the time corresponding to the zero point of the voltage in phase B,valve V8 becomes conducting. In response to this action, transformer T8is enabled to energize transformer T20, the,voltage whereof buildsin'phase with the voltage of phase B, and, at the zero point of the loadcurrent in phase B, transformer T2ll'overcomes the negative grid biasnormally aripplied to the grid of valve V2 by the biasing means DC 2.

The last-mentioned action fires valve V2, which thereupon" fires therectifier 24, associated with phase B, in the manner previouslydescribed in connection with the firing of rectifier 22. This firingaction of rectifier 24 occurs 60 electrical degrees after the firing ofrectifier 22, as will be understood, and throughout the balance of the(tl, Fig. 2) is high enough to overcome the negative bias normallyapplied to the grid of valve VI by the biasing means DCI and rendervalve VI conducting. As soon as valve Vi is rendered conductin phase Ais enabled to apply an ignitthrough the primary winding l8 of thewelding transformer to the other terminal of phase A. As will beappreciated, the energization of the welding transformer WT initiates aflow of current through the work.

Upon being rendered conducting, valve V1 also positive half cycle ofcurrent in phase A, the welding transformer WT is supplied with currentof a value equal to the vectorial sum of the currents flowing in phasesA and B.

The conductivity of valve V8 also enables the transformer T8 to energizethe sequence transformer Tl5, associated with the grid of valve V9. Aswill be understood from the description of the firing of valve V8,transformers T15 and T9 00- operate to fire valve V9 at the zero pointof voltage in phase C. This action energizes transformer T2l throughvalve V9 which, in turn, en ergizes transformer TM and thereby overcomesthe negative grid bias normally applied by the biasing means DC3 andfires the valve V3. Valve V3, in turn, fires the rectifier 26,associated with s phase C, which firing action occurs 60 electricaldegrees after the firing of rectifier 24.

At the conclusion of the positive half cycle of phase .A, rectifier 22ceases to pass current and remains non-conducting until the beginning ofa succeeding positive half cycle of current flow in phase A, in whichthe firing valve VI is again fired. As hereinafter described, this nextfiring of valve VI occurs at the time represented by the vertical lineT3 in Fig. 2, which time is displaced 1080 electrical degrees after theinitial firing thereof. Similarly, at the conclusion of the positivehalf cycle of phase B, rectifier 24 ceases to pass current and remainsnon-conducting until a time spaced 1080 electrical degrees from theinitial firing thereof. At the conclusion of the positive half cycle ofphase C, also, rectifier 26 ceases to pass current and remainsnon-conducting for a corresponding interval. The single firing of eachof rectifiers 22, 24 and 26 consequently passes through the weldingtransformer an impulse of current 300 electrical degrees in duration andthe value of which is equal to the vectoral sum of the currents flowingin the individual phases A, B and C. This impulse of current may bereferred to as a positive impulse of welding current.

The conductivity of valve V9, in addition to firing the rectifier 6.also enables the trans-' former T9 to energize the transformer TI Ii,and the potential developed by transformer TI6 is consequently appliedto the grid of valve VI 3. The connections for transformer TI6 are,however, such that the potential so built up is additive with respect tothe biasing means DCII). At the conclusion of the positive half cycle ofcurrent flow through transformer T9 and valve V9, the latter becomesnon-conducting, at which time the flux in transformer TIB is of amaximum value. The consequent rapid decay of such flux develops amomentary high opposite voltage in transformer TIE. This voltage isinitiated at approximately the vertical line marked TIE in Fig. 2, sincethe power factor of the circuit, including transformer T9, may beexpected to be somewhat higher than that of the welding load circuit,and this voltage of the transformer, which overcomes the biasing meansDCI3, persists until after transformer TI has rendered the plate ofvalve VI3 positive. Valve VI3 thus conducts current during the positivehalf cycle of phase A following the half cycle in which rectifier 22conducts current. This action enables the transformer TI3 to energizethe transformer TII, which initially builds up a voltage which isadditive with respect to the voltage of the biasing means DCIll,associated with valve VII). At the conclusion of the just-mentionedpositive half cycle of current flow in valve VI3, this valve becomesnon-conducting, The circuits including valve VI3 and transformers T9 andTIlI are less highly inductive than the load circuit for phase B.Consequently, valve VI3 becomes non-conducting slightly prior to thepoint designated t2 in Fig. 2. The interruption of current fiow throughvalve VI 3 causes a rapid decay of flux in transformer TH and develops ahigh momentary reverse voltage therein, which overcomes the biasingmeans DCIll. At the time t2 (Fig. 2), transformer TI I], which isreversely connected as compared to transformer T1, maintains the plateof valve VIII positive. Transformer TI! is still effective at the timet2, and consequently, at such time, valve VII) is rendered conductingand impresses the voltage of transformer TIO upon transformer T22, whichfires valve V4. Valve V4, in turn, fires rectifier 28, therebyinitiating a negative impulse of welding current. At the time t2, thevoltage of transformer T22, which is in phase with the voltage of phaseA, is high enough to overcome the biasing means DC4, and consequently,the firing of rectifier 28 occurs at the zero point of negative loadcurrent wave in phase A. The circuits by which valves V5 and V8 arefired, so as to correspondingly fire the main rec tifiers 30 and 32,associated with phase B and C, duplicate the corresponding circuitsassociated with valves V2 and V3, previously described, ,it being notedthat the connections for transformers TII and TI2 are the reverse ofthose for transformers T8 and T9, so that transformers TII and TI2 areeffective during negative half cycles of the corresponding phases.

As will be appreciated, the termination of the negative half cycle ofcurrent fiow in phase 0 terminates the negative impulse of weldingcurrent initiated at the time t2 in Fig. 2. In continuous operation, thenext positive impulse of load current is initiated at the time t3 inFig. 2, which corresponds to time tI, but is displaced 1080 electricaldegree therefrom. It will be noticed that phase A passes through twopositive half cycles in the interval between the conclusion of the abovedescribed positive impulse of load current and the time t3. The blockingcondenser 01, however, functions to maintain valve V1 in anon-conducting condition and prevents the firing of rectifier 22 duringthe justmentioned two positive half cycles. As previously mentioned. thepeaking transformer T4 develops its critical potential at a time whichcoincides with the beginning of the positive half cycle of current flowin phase A. Consequently,-

condenser Cl may time out at any time in the interval between thevertical lines designated t4 and t3 in Fig. 2. This is. for the reasonthat if valve V1 is blocked by condenser 01, at the time represented bythe line t4, the critical potential developed at such time bytransformer T4 is ineffective to fire valve VI. Transformer T4 againdevelops a critical potential at a, time displaced electricaldegreesfrom the time t4. This potential, however, is ineffective since at thetime in question the plate of valve V! is negative. Consequently, havingpassed the time t4, it is only necessary that condenser 01 time outbefore the time t3 is reached. In order to allow for some variation intiming, it is preferred to adjust condenser 01, so that it times out atapproximately the time represented by the line t5, so that a variationin the timing thereof in either 'direction of approximately a full halfcycle does not alter the operation of the system.

It will be understood, therefore, that when valve V1 is initially fired,it charges condenser 01, which thereupon blocks valve VI and enablescondenser CT to start discharging through the obvious local circuitassociated therewith, which includes the variable resistor RI. As soonas the energy of condenser C1 is dissipated to a predetermined degree,however, valve VI again becomes subject to the action of transformer T4and consequently, if the starting switch S is still closed at the timet3, another complete cycle, comprising a pair of respectively oppositeimpulses of load current, is initiated, all as described above. Thus, solong as the starting switch S is maintained closed, alternately oppositeimpulses of load current are continuously supplied to the weldingtransformer WT. Also. it is believed to be evident that the opening ofswitch S may occur substantially instantaneously after the firing ofvalve V'I, since transformer T1 is required to be energized only longenough to fire valve V1 and maintain transformer TI4 energized longenough to firevalve V8. Thererent.

Although only one specific embodiment of the invention has beendescribed in detail, it will be appreciated that various modificationsin the iorm, number and arrangement or parts may be 7 madewithout'departing from the spirit and scope of the invention. a

what is claimed is:

1. In a timingcontrol sy'stemior a plurality oi translating means forassociation with a source oi! power which delivers a succession ofcyclical impulses of alternately opposite polarity, valve meansindividual to each of said translating means, means for actuating one ofsaid valve means so as to effect an operation of the correspondingtranslating means for delivering an im-' pulse of one polarity, meansoperated as a consequence of the operation of said one valve means foractuating another of said valve means, said last valve means operatingthe corresponding translating means for delivering an impulse of theopposite polarity at least a cycle and onehalf after the delivery ofsaid first impulse, and

. means for causing the operation of said translating means to occurduring respectively spaced opposite pulsations of said source at least acycle and one-half from each such operation.

2. In a timing control system for a plurality of translating means forassociation with a source of power which delivers a succession ofcyclical impulses of alternately opposite polarity, one said translatingmeans corresponding to impulses of one polarity and another Saidtranslating means corresponding to impulses of opposite polarity, valvemeans individual to each of said translating means, means for actuatingone of said valve means so as to effect an operation of thecorresponding translating means for delivering an impulse of onepolarity, and means operthe combination of a plurality of translatingmeans, one said translating means being individual to each said phaseand to each half cycle of said phase. valve means individual to each ofsaid translating means, means for actuating one of said valve means soas to effect an operation of the corresponding translating means, andmeans operated as a consequence of the operation of said one valve meansfor actuating the remaining ones of said valve means.

4. In a timing control system for association with a, multiphasealternating current source, the combination of a plurality oftranslating means, one said translating means being individual to eachsaid phase and to each half cycle of said phase, valve means individualto each of said translating means, means for actuating the valve meanscorresponding to the half cycles of like polarity of the several phases,and means operated as a consequence of the operation of saidlastmentioned valve means for actuating the remaining ones of said valvemeans.

5. In a timing control system for association ing re-operatlon oisaidone valve means for a predetermined interval after the operationthereof.

6. In a timing control system for association with a multiphasealternating current source, the

combination ota plurality of translating means,

erated as a consequence of the operation oi. said one valve means Ioractuating the remaining ones of said valve means, and means iforpreventing re-operation of said one valve means for a predeterminedinterval after the operation thereof, said one valve means beingeflective after the timing out of said preventing means to initiate afurther sequential operation of said series of valve means.

7. In a timing control system for association with a multiphasealternating current source. the combination of a plurality oftranslating means, one said translating means being individual to eachsaid phase andto each half cycle of said phase, valve means individualto each of said translating means, means for actuating one of said valvemeans so as to effect an operation of the corresponding translatingmeans, means operated as a consequence of the operation of said onevalve means for actuating the remaining ones of said valve means, andmeans for preventing re-operation of said one valve means for apredetermined interval after the operation thereof, said preventingmeans being effective to delay said re-operation for an interval suchthat successive operations of said one valve means are spaced in excessof 360 electrical degrees.

8. In a control system for association with a multiphase alternatingcurrent source, a pair of reversely connected rectifiers individual toeach phase and operable respectively to transmit current during oppositehalf cycles of such phase, said pairs of rectifiers being connected totrans- ,late power from said source into a succession of impulses ofalternately opposite polarity, each impulse representing the vectorialsum of impulses of like polarity of the individual phases, valve meansindividual to each rectifier for rendering the same conducting, andsequencing means for first actuating the valve means associated with therectifiers of a half cycle of one polarity of said source and forthereafter actuating the valve means associated with the rectifierscorresponding to the opposite half cycles of said source.

9. In a control system for association with a multiphase alternatingcurrent source, a pair of reversely connected rectifiers individual toeach phase and operable respectively to transmit current during oppositehalf cycles of such phase, said pairs of rectifiers being connected totranslate power from said source into a succession of impulses ofalternately opposite polarity, each 1m pulse representing the vectorialsum of impulses of like polarity of the individual phases, valve meansindividual to each rectifier for rendering the same conducting,sequencing means for first actuating the valve means associated with therectifiers of a half cycle of one polarity of said source and forthereafter actuating the valve means associated with the rectifierscorresponding to the opposite half cycles of said source, starting meansfor actuating the operation of the first valve means of the series, andsaid sequence means serving to cause the remainder of the valve means tooperate in sequence as a consequence of the operation of said one valvemeans.

10. In a control system for association with a multiphase alternatingcurrent source, a pair of reversely connected rectifiers individual toeach phase and operable respectively to transmit current during oppositehalf cycles of such phase,

said pairs of rectifiers being connected to translate power from saidsource into a succession of impulses oi! alternately opposite polarity,each impulse representing the vectorial sum of impulses of like polarityof the individual phases, valve means individual to each rectifier forrendering the same conducting, and sequencing means for first actuatingthe valve means associated with the rectifiers of a half cycle of onepolarity of said source and for thereafter actuating the valve meansassociated with the rectifiers corresponding to the opposite half cyclesof said source, the rectifiers corresponding to said opposite halIcycles of the source being operated in the same order as said rectifierscorresponding to the half cycles of said one polarity.

11. In a control system for association with a multiphase alternatingcurrent source, a pair of reversely connected rectifiers individual toeach phase and operable respectively to transmit current during oppositehalf cycles of such phase, said pairs of rectifiers being connected totranslate power from said source into a succession of impulses ofalternately opposite polarity, each impulse representing the vectorialsum of impulses of like polarity of the individual phases, valve meansindividual to each rectifier for controlling the conductivity of thesame, and sequencing means for said valve means operable to actuate thesame so as to sequentially cause conduction through the rectifiersassociated with half cycles of the source of one polarity and forthereafter causing conducting through the rectifiers corresponding tothe opposite half cycles of the source.

12. In a control system for a work circuit associated with a multiphasealternating current supply source, the severalphases whereof aredisplaced but overlap as to time, the combination of means electricallyconnecting said phases to said work circuit so that said work circuitreceives dzhe combined current outputs of said phases as a succession ofimpulses of alternately opposite polarity, each said impulse being asummation of current components oi! like polarity supplied by theindividual phases, said means ineluding means individual to each saidphase for controlling current flow in the corresponding phase, and meansfor operating said individual means in succession.

13. In a control system for a work circuit associated with a multiphasealternating current supply source, the several phases whereof aredisplaced but overlap as to time, the combination of means electricallyconnecting said phases to said work circuit so that said work circuitreceives the combined current outputs of said phases as a succession ofimpulses of alternately opposite polarity, each said impulse being asummation of current components of like polarity supplied by theindividual phases, said means including electric valve means individualto each said phase, and means for altering the conductivity of saidvalve means in predetermined succession.

14. In a control system for a work circuit associated with 'a multiphasealternating current supply source, the several phases whereof aredisplaced but overlap as to time, the combination of means electricallyconnecting said phases to said work circuit so that said work circuitreceives the combined current outputs of said phases as a succession ofimpulses of alternately opposite polarity, each said impulse being asummation of current components of like polarity supplied by theindividual phases, said means including a pair of reversely connectedelectric valve means individual to each said phase, the first valve ofeach pair being disposed to conduct current during half cycles of onepolarity and the second valve of each pair being disposed to conductcurrent during half cycles of the opposite polarity, and means forsuccessively actuating the first valves of all of the pairs and forthereafter successively actuating the second valves of all of the pairs.

15. In a control system for a work circuit associated with a multiphasealternating current supply source, the several phases whereof aredisplaced but overlap as to time, the combination of means electricallyconnecting said phases to said work circuit so that said work circuitreceives the combined current outputs of said phases as a succession ofimpulses of alternately opposite polarity, each said impulse being asummation of current components of like polarity supplied by theindividual phases, said means including a pair of reversely connectedelectric valve means individual to each said phase, the first valve ofeach pair being disposed to conduct current during half cycles of onepolarity and the second valve of each pair being disposed to conductcurrent during half cycles of the opposite polarity, and means forsuccessively actuating the first valves of all of the pairs and forthereafter successively actuating the second valves of all of the pairs,the said second valves being operated in the same order as said firstvalves.

GUSTAV E. UNDY.

